Field
The embodiments generally relate to chromophore compounds comprising novel azo-benzene type structures. The chromophores are useful in photochromic compositions comprising a polymer matrix and at least chromophore, wherein the chromophore comprises a novel azo-benzene type structure. The photochromic composition is photoresponsive upon irradiation by at least one wavelength of light across the visible light spectrum. Photochromic devices which comprise the novel azo-benzene type chromophore compound show photoresponsive properties, including high diffraction efficiency, high photoinduced birefringence, and fast response time. The photochromic composition may include a liquid crystal.
Description of the Related Art
Holographic memories have attracted much attention due to their potential use in three-dimensional display applications and high capacity data storage mediums. There are several different types of optical information recording media capable of storing holographic information, which include photorefractive materials and photochromic materials. Both photochromic and photorefractive materials have many promising applications, such as high-density optical data storage, dynamic holography, optical image processing, phase conjugated mirrors, optical computing, parallel optical logic, and pattern recognition. Particularly, high diffraction efficiency can contribute significantly to high-density optical data storage or holographic display applications.
Originally, the photorefractive effect was found in a variety of inorganic electro-optical (EO) crystals, such as LiNbO3. In these materials, the mechanism of a refractive index modulation by the internal space-charge field is based on a linear electro-optical effect. In 1990 and 1991, the first organic photorefractive crystal and polymeric photorefractive materials were discovered and reported. Some relevant information related to these materials can be found in U.S. Pat. No. 5,064,264, the contents of which are hereby incorporated by reference in their entirety. Organic photorefractive materials offer many advantages over the original inorganic photorefractive crystals, such as large optical nonlinearities, low dielectric constants, low cost, lightweight, structural flexibility, and ease of device fabrication. However, researchers have found that large scale organic photorefractive devices easily breakdown, and they have been unable to design organic photorefractive compositions that do not exhibit this high breakdown issue.
Similarly, photochromic materials have also been around for decades. The photochromic effect occurs when a compounds optical properties, such as absorption, emission, reflection, birefringence or scattering, are reversibly modified by means of a photoinduced physical and/or chemical processes. Typical organic photochromic materials are polymers having an azo-benzene structure. Relevant literature includes U.S. Pat. No. 5,641,846, U.S. Pat. No. 7,951,922, and S. Xie, A. Natansohn and P. Rochon, Chem. Rev., vol. 5 (1993) p. 403-411, “Recent Development in Aromatic Azo Polymers Research”, T. Bieringer, R. Wuttke, D. Haarer, U. Gesner and J. Rubner, Macromol. Chem. Phys., vol. 196 (1995) p. 1375-1390, “Relaxation of holographic gratings in liquid-crystalline side chain polymers with azo chromophores”, and A. Natansohn and P. Rochon, ACS Symposium Series, vol. 672 (1997) p. 236-250, “Azobenzene-containing polymers: digital and holographic storage” and A. Natansohn, P. Rochon, X. Meng, C. Barrett, T. Buffeteau, S. Bonenfant and M. Pezolet, Macromolecules, vol. 31 (1998) p. 1155-1161, “Molecular addressing Selective photoinduced cooperative motion of polar ester groups in copolymers containing azobenzene groups”. 
The photochromic composition may be made by mixing molecular components that provide desirable individual properties into a host polymer matrix. However, many of the previously prepared compositions failed to show good photochromic performances, (e.g., high diffraction efficiency, fast response time and long-term stability). Efforts have been made, therefore, to provide compositions which show high diffraction efficiency, fast response time and long stability. However, a photochromic composition that provides all the various properties required for practical application such as sensitivity, response speed, long-term storage stability, and repeatability has not yet been found.